The present invention relates to a method for checking the plausibility of a NOx sensor in an SCR catalytic converter system having at least one first SCR catalytic converter device and having at least one second SCR catalytic converter device and having in each case one dosing point for a reducing agent solution for the SCR catalytic converter devices upstream of the respective SCR catalytic converter device. The invention also relates to a computer program, to a machine-readable storage medium, and to an electronic control unit, which are provided for carrying out the plausibility checking method.
To comply with the legally prescribed exhaust-gas limit values during the operation of motor vehicles, complex exhaust-gas aftertreatment systems are used. More stringent regulations in the field of the diagnosis of emissions-relevant components necessitate, in the context of so-called on-board diagnosis (OBD), monitoring of all exhaust-gas aftertreatment components and of the sensors used with regard to compliance with the OBD limit values.
For the reduction of nitrogen oxides (NOx), SCR (Selective Catalytic Reduction) catalytic converters are known. The basic principle of the SCR catalytic converter consists in nitrogen oxide molecules being reduced on the catalytic converter surface, in the presence of ammonia (NH3) as reducing agent, to form elementary nitrogen. SCR catalytic converters that are known nowadays store NH3 on the catalytic converter surface. The NH3 stored on the catalytic converter surface is described as the NH3 fill level. DE 10 2012 201 749 A1 has disclosed a method for the diagnosis of the NH3 storage capacity of the SCR catalytic converter as a feature for the aging of or damage to the catalytic converter, wherein, prior to the start of the diagnosis or of an overdosing phase (superstoichiometric reducing agent dosing), conditioning of the SCR catalytic converter is performed in order to set a working point in the form of a certain NH3 fill level as a starting point for the diagnosis.
To attain higher conversion rates in the nitrogen oxide reduction in the exhaust tract, systems are already known which comprise two separate SCR catalytic converter devices connected in series. The laid-open specifications DE 10 2013 203 580 A1 and DE 10 2012 221 905 A1 are concerned with operating methods for exhaust-gas aftertreatment systems with two SCR catalytic converter devices.